These fastener drivers are powered, for instance, electrically, whereby at least one drive spring serves as the energy storage unit for the driving tappet, and this drive spring can be tensioned by means of an electrically operated tensioning mechanism. An advantage of such fastener drivers is their simple construction, which makes them inexpensive to produce.
A fastener driver configured as an electric nailer is disclosed in U.S. Pat. No. 3,810,572. This fastener driver has a driving hammer comprising a threaded shaft section that faces away from the driving direction and a hammer section that is positioned in the driving direction. Part of the threaded shaft section is arranged axially inside a drive spring element. A sleeve arranged radially on the outside around the non-rotatable driving hammer can be made to rotate by means of a drive motor, whereby balls that run in the sleeve engage with the thread of the threaded section in order to move the driving hammer axially against the drive spring element so as to tension the latter. For purposes of triggering a fastener driving procedure, a first latching sleeve is provided that is arranged so as to be movable on the outside of the sleeve and that can be moved axially by means of the trigger in order to release latching balls radially to the outside. Another latching sleeve that is arranged on the outside of the first latching sleeve controls the radial disengagement of the balls that engage with the thread. Once a fastener driving procedure has been triggered, the driving hammer, along with its hammer section and its shaft section, is moved in the driving direction by the drive spring element.
A drawback of this fastener driver is, on the one hand, that the construction of the three sleeves is very complex, thus making the fastener driver more expensive. On the other hand, when the fastener driver is triggered, the entire force of the drive spring is exerted for a brief moment onto a very small surface area at the edge of the thread where the last latching ball is disengaged. This entails the risk that the edge of the thread might break.
German patent application DE 32 37 087 A1 discloses a fastener driver configured as an electric tacker. With this fastener driver, a driving tappet configured as a firing pin is moved into a tensioned position against a drive spring by a rotating electric motor. For this purpose, the driving tappet is provided with teeth that can be made to engage with a threaded spindle that can be driven by an electric motor. In a tensioned end position of the drive spring, the threaded spindle swivels out of its engagement with the teeth on the driving tappet. In this tensioned position, the driving tappet can be locked by means of a locking member. In order to trigger a fastener driving procedure, a trigger switch such as a triggering lever or a pushbutton has to be actuated by means of which the locking member is released from its locked position on the driving tappet. The fastening elements that can be driven with the electric tacker can be stored, for example, in a cartridge.
A disadvantage of this fastener driver is that its construction with a controlled swiveling spindle is quite laborious and expensive. Moreover, a swiveling spindle is larger and heavier, which is a serious a drawback for a hand-held fastener driver.